The publication JP-58-012806 describes a completely ceramic spike for winter tires. The spike is a polygon in cross-section, with the contact surface of the spike tip being particularly polygonal. According to the drawings of the publication, the contact surface of the spike tip is either a sharp-angled quadrangle or an octagon. The spike also includes a bottom flange made of the same ceramic material, with the same shape as the respective shape of the contact surface of the tip.
According to the publication JP-58-012806, the disclosed design is chosen primarily because of the manufacturing technique. But, it is maintained that the strength and grip of the spike are also improved in comparison with a spike that is round in cross-section, but otherwise has the same type of structure. In the publication JP-58-012806, the spike material is mainly composed of aluminum oxide Al2O3, and the durability of this type of material is not sufficient in practice. This type of spike is strongly inclined when driving, particularly if the tire tread is made of a relatively soft rubber, as is the trend nowadays, which means that the grip is remarkably reduced and the spikes may even become detached. If a spike of this type is made of a sufficiently hard, impact-resistant and wear-resistant hard metal, the weight of the anti-slip element becomes remarkably heavy, which means that the wearing of the road surface is intensive and the rubber tread of the tire is easily damaged. The design according to the publication JP-58-012806 makes it difficult to install spikes by automatic devices. The design also results in a swift tearing of the tire tread in the vicinity of the spike when driving, which, as a consequence, can cause the spikes to fall off.
The publication DE-1 202 156 and U.S. Pat. No. 3,230,997 each disclose an anti-skid spike that includes a circular body made from, for example, steel, aluminum or plastic, and a piece of sintered carbide arranged inside the body. The piece of sintered carbide has the form of a square. According to the publications, the reason for using the quadratic form is to improve the fixing of the sintered carbide piece inside the body.
The publication WO-99/56976 discloses an anti-skid spike with a hard cermet piece that has a geometric cross-sectional shape, a limited number of symmetry levels and a changing cross-sectional area from the outer head to the inner head such that the hard cermet piece expands towards the bottom flange of the spike. The publication mentions several different cross-sectional shapes of the hard cermet piece, such as a triangle, a rectangle, an ellipse, a semi rectangle, a semicircle, a quadrangle, and an octagon, with all such shapes particularly equal in significance.
As regards the shape of the bottom flange of the anti-skid spike disclosed in WO-99/56976 , it is only said that it may be asymmetrical with respect to one lengthwise plane with a length and a width that are mutually different. According to the drawings of the publication, the bottom flange includes two opposite straight sides, either in parallel or at a sharp angle with respect to each other. It is also mentioned that intermediate shapes between these two are possible, but the specification does not offer a more detailed description, only a general remark. Neither of the shapes of the sides of the bottom flange are quadrangles.
The publication WO-99/56976 also recommends the use of a rib in the lengthwise direction of the spike, but without a top bowl. Further, as shown in the drawings, the longer dimension of the bottom flange of the publication WO-99/56976 can be positioned either in the circumferential direction of the tire, in which case it is suited to urban driving as described in the publication, or perpendicular to the circumferential direction, in which case it is suited to driving on country roads as described in the publication.
The publication DE-23 42 743 describes an ice stud designed for winter tires of vehicles, wherein the ice stud comprises an element made of one material and is rectangular in cross-section. The shape of the ice stud is the same along the whole length of the anti-slip element. This kind of stud goes easily deeper in the tire and tends to incline excessively during speed and/or direction changes, which results in a weak grip on a slippery road surface. These kinds of ice studs can easily detach from the tire tread during usage. As the only objective of the invention, the publication mentions a decrease in the wearing of the road surface.
The publication US 2002/0050312 discloses a studded winter tire, where the stud has an elongate bottom part with a shape other than round, and the shape has a lengthwise axis and an elongate top part other than round. The shape of the bottom part and top part of the stud is nearly an ellipse, or an oblong shape resembling an ellipse. In the middle of the tire rolling surface, the lengthwise axes of the top parts of the studs are in a position parallel to the tire axis, and the lengthwise axes of the bottom parts of the studs are arranged in the circumferential direction of the tire.